Surgical access system and related methods

ABSTRACT

A system for accessing a surgical target site and related methods, involving an initial distraction system for creating an initial distraction corridor, and an assembly capable of distracting from the initial distraction corridor to a secondary distraction corridor and thereafter sequentially receiving a plurality of retractor blades for retracting from the secondary distraction corridor to thereby create an operative corridor to the surgical target site, both of which may be equipped with one or more electrodes for use in detecting the existence of (and optionally the distance and/or direction to) neural structures before, during, and after the establishment of an operative corridor to a surgical target site.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/466,398, filed May 8, 2012, which is a continuation of U.S. patentapplication Ser. No. 12/649,604 filed Dec. 30, 2009 (now U.S. Pat. No.8,182,423), which is a continuation of U.S. patent application Ser. No.12/635,418 filed Dec. 10, 2009 (now U.S. Pat. No. 8,192,356), which is acontinuation of U.S. patent application Ser. No. 12/428,081, filed Apr.22, 2009, which is a continuation of U.S. patent application Ser. No.10/608,362 filed Jun. 26, 2003 (now U.S. Pat. No. 7,582,058), whichclaims priority to U.S. Provisional Patent Application Ser. No.60/392,214, filed Jun. 26, 2002, the entire contents of theseapplications are hereby expressly incorporated by reference into thisdisclosure as if set forth fully herein. The present application alsoincorporates by reference the following co-assigned patent applicationsin their entireties: PCT App. Ser. No. PCT/US02/22247, entitled “Systemand Methods for Determining Nerve Proximity, Direction, and PathologyDuring Surgery,” filed on Jul. 11, 2002 (published as WO03/005887); PCTApp. Ser. No. PCT/US02/30617, entitled “System and Methods forPerforming Surgical Procedures and Assessments,” filed on Sep. 25, 2002(published as WO 03/026482); PCT App. Ser. No. PCT/US02/35047, entitled“System and Methods for Performing Percutaneous Pedicle IntegrityAssessments,” filed on Oct. 30, 2002 (published as WO/03037170); and PCTApp. Ser. No. PCT/US03/02056, entitled “System and Methods forDetermining Nerve Direction to a Surgical Instrument,” filed Jan. 15,2003 (published as WO/2004064634).

BACKGROUND

I. Field

The present invention relates generally to systems and methods forperforming surgical procedures and, more particularly, for accessing asurgical target site in order to perform surgical procedures.

II. Description of Related Art

A noteworthy trend in the medical community is the move away fromperforming surgery via traditional “open” techniques in favor ofminimally invasive or minimal access techniques. Open surgicaltechniques are generally undesirable in that they typically requirelarge incisions and high amounts of tissue displacement to gain accessto the surgical target site, which produces concomitantly high amountsof pain, lengthened hospitalization (increasing health care costs), andhigh morbidity in the patient population. Less-invasive surgicaltechniques (including so-called “minimal access” and “minimallyinvasive” techniques) are gaining favor due to the fact that theyinvolve accessing the surgical target site via incisions ofsubstantially smaller size with greatly reduced tissue displacementrequirements. This, in turn, reduces the pain, morbidity and costassociated with such procedures. The access systems developed to date,however, fail in various respects to meet all the needs of the surgeonpopulation.

One drawback associated with prior art surgical access systems relatesto the ease with which the operative corridor can be created, as well asmaintained over time, depending upon the particular surgical targetsite. For example, when accessing surgical target sites located beneathor behind musculature or other relatively strong tissue (such as, by wayof example only, the psoas muscle adjacent to the spine), it has beenfound that advancing an operative corridor-establishing instrumentdirectly through such tissues can be challenging and/or lead to unwantedor undesirable effects (such as stressing or tearing the tissues). Whilecertain efforts have been undertaken to reduce the trauma to tissuewhile creating an operative corridor, such as (by way of example only)the sequential dilation system of U.S. Pat. No. 5,792,044 to Foley etal., these attempts are nonetheless limited in their applicability basedon the relatively narrow operative corridor. More specifically, based onthe generally cylindrical nature of the so-called “working cannula,” thedegree to which instruments can be manipulated and/or angled within thecannula can be generally limited or restrictive, particularly if thesurgical target site is a relatively deep within the patient.

Efforts have been undertaken to overcome this drawback, such as shown inU.S. Pat. No. 6,524,320 to DiPoto, wherein an expandable portion isprovided at the distal end of a cannula for creating a region ofincreased cross-sectional area adjacent to the surgical target site.While this system may provide for improved instrument manipulationrelative to sequential dilation access systems (at least at deep siteswithin the patient), it is nonetheless flawed in that the deployment ofthe expandable portion may inadvertently compress or impinge uponsensitive tissues adjacent to the surgical target site. For example, inanatomical regions having neural and/or vasculature structures, such ablind expansion may cause the expandable portion to impinge upon thesesensitive tissues and cause neural and/or vasculature compromise, damageand/or pain for the patient.

This highlights yet another drawback with the prior art surgical accesssystems, namely, the challenges in establishing an operative corridorthrough or near tissue having major neural structures which, ifcontacted or impinged, may result in neural impairment for the patient.Due to the threat of contacting such neural structures, efforts thus farhave largely restricted to establishing operative corridors throughtissue having little or substantially reduced neural structures, whicheffectively limits the number of ways a given surgical target site canbe accessed. This can be seen, by way of example only, in the spinalarts, where the exiting nerve roots and neural plexus structures in thepsoas muscle have rendered a lateral or far lateral access path(so-called trans-psoas approach) to the lumbar spine virtuallyimpossible. Instead, spine surgeons are largely restricted to accessingthe spine from the posterior (to perform, among other procedures,posterior lumbar interbody fusion (PLIF)) or from the anterior (toperform, among other procedures, anterior lumbar interbody fusion(ALIF)).

Posterior-access procedures involve traversing a shorter distance withinthe patient to establish the operative corridor, albeit at the price ofoftentimes having to reduce or cut away part of the posterior bonystructures (i.e. lamina, facets, spinous process) in order to reach thetarget site (which typically comprises the disc space). Anterior-accessprocedures are relatively simple for surgeons in that they do notinvolve reducing or cutting away bony structures to reach the surgicaltarget site. However, they are nonetheless disadvantageous in that theyrequire traversing through a much greater distance within the patient toestablish the operative corridor, oftentimes requiring an additionalsurgeon to assist with moving the various internal organs out of the wayto create the operative corridor.

The present invention is directed at eliminating, or at least minimizingthe effects of, the above-identified drawbacks in the prior art.

SUMMARY

The present invention accomplishes this goal by providing a novel accesssystem and related methods which involve: (1) distracting the tissuebetween the patient's skin and the surgical target site to create anarea of distraction (otherwise referred to herein as a “distractioncorridor”); (2) retracting the distraction corridor to establish andmaintain an operative corridor; and/or (3) detecting the existence of(and optionally the distance and/or direction to) neural structuresbefore, during and after the establishment of the operative corridorthrough (or near) any of a variety of tissues having such neuralstructures which, if contacted or impinged, may otherwise result inneural impairment for the patient.

As used herein, “distraction” or “distracting” is defined as the act ofcreating a corridor (extending to a location at or near the surgicaltarget site) having a certain cross-sectional area and shape(“distraction corridor”), and “retraction” or “retracting” is defined asthe act of creating an operative corridor by increasing thecross-sectional area of the distraction corridor (and/or modifying itsshape) with at least one retractor blade and thereafter maintaining thatincreased cross-sectional area and/or modified shape such that surgicalinstruments can be passed through operative corridor to the surgicaltarget site. It is expressly noted that, although described hereinlargely in terms of use in spinal surgery, the access system of thepresent invention is suitable for use in any number of additionalsurgical procedures, including those wherein tissue having significantneural structures must be passed through (or near) in order to establishan operative corridor.

According to one aspect, the present invention provides a surgicalaccess system having an initial tissue distraction assembly and a pivotlinkage assembly forming part of a secondary distraction assembly and aretraction assembly. The secondary distraction assembly includes firstand second distraction arms forming part of the pivot linkage assembly,first and second speculum blades extending through receiving passagewaysformed within the first and second distraction arms, and a handleassembly forming part of the pivot linkage. As will be described below,the distraction arms may be advanced over the initial distractionassembly such that the speculum blades are passed into the tissue to besecondarily distracted. Thereafter, the handle assembly may be activatedto perform the necessary distraction. That is, the handle assembly canbe manipulated by a user to move the first and second distraction armsaway from one another, which will at the same time move the distal endsof the speculum blades to create a full distraction corridor.

After the secondary distraction, a pair of retractors blades may beintroduced into the distraction corridor and positioned to create anoperative corridor to the surgical target site. In a preferredembodiment, retractor blade is introduced first and positioned such thatits distal end is generally located towards the posterior region of thespinal target site, which forms a useful barrier to prevent any exitingnerve roots 30 from entering the surgical target site, as well as toprevent any surgical instruments from passing outside the surgicaltarget site and into contact with the exiting nerve roots 30 or othersensitive tissue. The retractor blade may thereafter be introduced andmoved in a generally anterior direction away from the retractor blade,effectively creating the operative corridor. The retractor blades may belocked in relation to the pivot linkage assembly in any number ofsuitable fashions, including but not limited to the use of the nut-boltassemblies well known in the art. To lock the retractor blades inrelation to the surgical target site, optional locking members may beadvanced through receiving passageways formed in one or more of theretractor blades such that a distal region of the locking member isbrought into a press-fit, secure engagement between the adjacentvertebral bodies to thereby maintain the respective retractor blade inposition. With the operative corridor established, any of a variety ofsurgical instruments, devices, or implants may be passed through and/ormanipulated at or near the surgical target site depending upon the givensurgical procedure.

According to yet another aspect of the present invention, any number ofdistraction assemblies and/or retraction assemblies (including but notlimited to those described herein) may be equipped to detect thepresence of (and optionally the distance and/or direction to) neuralstructures during the steps tissue distraction and/or retraction. Toaccomplish this, one or more stimulation electrodes are provided on thevarious components of the distraction assemblies and/or retractionassemblies, a stimulation source (e.g. voltage or current) is coupled tothe stimulation electrodes, a stimulation signal is emitted from thestimulation electrodes as the various components are advanced towardsthe surgical target site, and the patient is monitored to determine ifthe stimulation signal causes muscles associated with nerves or neuralstructures within the tissue to innervate. If the nerves innervate, thisindicates that neural structures may be in close proximity to thedistraction and/or retraction assemblies.

This monitoring may be accomplished via any number of suitable fashions,including but not limited to observing visual twitches in muscle groupsassociated with the neural structures likely to found in the tissue, aswell as any number of monitoring systems. In either situation(traditional EMG or surgeon-driven EMG monitoring), the access system ofthe present invention may advantageously be used to traverse tissue thatwould ordinarily be deemed unsafe or undesirable, thereby broadening thenumber of manners in which a given surgical target site may be accessed.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a perspective view of a surgical access system according toone aspect of the present invention;

FIG. 2 is a perspective view of an initial tissue distraction assemblyforming part of a surgical access system according to the presentinvention;

FIGS. 3-4 are exploded views detailing the distal portions of theinitial tissue distraction assembly shown in FIG. 2;

FIG. 5 is a perspective view of a pivot linkage assembly equipped withspeculum blades according to the present invention;

FIG. 6 is a side view of the pivot linkage assembly shown in FIG. 5;

FIGS. 7-8 are perspective views showing the pivot linkage assembly ofFIG. 5 in use;

FIGS. 9-10 are perspective views of a retractor blade forming part of asurgical access system according to the present invention;

FIG. 11 is a perspective view of a locking member for use with theretractor blade of FIGS. 9-10 according to the present invention;

FIG. 12 is a perspective view of an exemplary nerve monitoring systemcapable of performing nerve monitoring before, during and after thecreating of an operative corridor to a surgical target site using thesurgical access system in accordance with the present invention;

FIG. 13 is a block diagram of the nerve monitoring system shown in FIG.12;

FIGS. 14-15 are screen displays illustrating exemplary features andinformation communicated to a user during the use of the nervemonitoring system of FIG. 12;

FIGS. 16-33 illustrate the various method steps (some optional) involvedin accessing (by way of example only) a surgical target site in thespine according to the present invention.

DETAILED DESCRIPTION

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. It is furthermore to be readily understood that,although discussed below primarily within the context of spinal surgery,the surgical access system of the present invention may be employed inany number of anatomical settings to provide access to any number ofdifferent surgical target sites throughout the body. The surgical accesssystem disclosed herein boasts a variety of inventive features andcomponents that warrant patent protection, both individually and incombination.

The present invention is directed at a novel surgical access system andrelated methods which involve creating a distraction corridor to asurgical target site, thereafter retracting the distraction corridor toestablish and maintain an operative corridor to the surgical targetsite, and optionally detecting the existence of (and optionally thedistance and/or direction to) neural structures before, during and/orafter the formation of the distraction and/or operative corridors. Thesteps of distraction followed by retraction are advantageous becausethey provide the ability to more easily position an operativecorridor-establishing device through tissue that is strong, thick orotherwise challenging to traverse in order to access a surgical targetsite. The various distraction systems of the present invention areadvantageous in that they provide an improved manner of atraumaticallyestablishing a distraction corridor prior to the use of the retractionsystems of the present invention. The various retractor systems of thepresent invention are advantageous in that they provide an operativecorridor having improved cross-sectional area and shape (includingcustomization thereof) relative to the prior art surgical accesssystems. Moreover, by optionally equipping the various distractionsystems and/or retraction systems with one or more electrodes, anoperative corridor may be established through (or near) any of a varietyof tissues having such neural structures which, if contacted orimpinged, may otherwise result in neural impairment for the patient.

FIG. 1 illustrates a surgical access system 10 according to one aspectof the present invention. The surgical access system 10 includes aninitial tissue distraction assembly 12 and a pivot linkage assembly 14forming part of a secondary distraction assembly and a retractionassembly. The secondary distraction assembly includes first and seconddistraction arms 16, 18 forming part of the pivot linkage assembly 14,first and second speculum blades 20, 22 extending through receivingpassageways formed within the first and second distraction arms 16, 18,and a handle assembly 24 forming part of the pivot linkage 14. As willbe described below, the distraction arms 16, 18 may be advanced over theinitial distraction assembly 12 such that the speculum blades 20, 22 arepassed into the tissue to be secondarily distracted. Thereafter, thehandle assembly 24 may be activated to perform the necessarydistraction. That is, the handle assembly 24 can be manipulated by auser to move the first and second distraction arms 16, 18 away from oneanother, which will at the same time move the distal ends of thespeculum blades 20, 22 to create a full distraction corridor.

After the secondary distraction, a pair of retractors blades 26, 28 maybe introduced into the distraction corridor and positioned to create anoperative corridor to the surgical target site. In a preferredembodiment, retractor blade 26 is introduced first and positioned suchthat its distal end is generally located towards the posterior region ofthe spinal target site, which forms a useful barrier to prevent anyexiting nerve roots 30 from entering the surgical target site, as wellas to prevent any surgical instruments from passing outside the surgicaltarget site and into contact with the exiting nerve roots 30 or othersensitive tissue. The retractor blade 28 may thereafter be introducedand moved in a generally anterior direction away from the retractorblade 26, effectively creating the operative corridor. The retractorblades 26, 28 may be locked in relation to the pivot linkage assembly 14in any number of suitable fashions, including but not limited to the useof the nut-bolt assemblies 32, 34 well known in the art. To lock theretractor blades 26, 28 in relation to the surgical target site,optional locking members 36 may be advanced through receivingpassageways formed in one or more of the retractor blades 26, 28 suchthat a distal region of the locking member 36 is brought into apress-fit, secure engagement between the adjacent vertebral bodies tothereby maintain the respective retractor blade 26, 28 in position. Withthe operative corridor established, any of a variety of surgicalinstruments, devices, or implants may be passed through and/ormanipulated at or near the surgical target site depending upon the givensurgical procedure.

Distraction

FIG. 2 illustrates the initial tissue distraction assembly 12, which isdesigned to perform an initial distraction of tissue from the skin ofthe patient down to or near the surgical target site. The initial tissuedistraction assembly 12 may be constructed from any number of materialssuitable for medical applications, including but not limited toplastics, metals, ceramics or any combination thereof. Depending on theconstruction, some or all of the tissue distraction assembly 12 may bedisposable (i.e. single use) and/or reusable (i.e. multi-use).

The initial tissue distraction assembly 12 may include any number ofcomponents capable of performing the necessary initial distraction. Byway of example, with combined reference to FIGS. 2-4, this may beaccomplished by providing the initial distraction assembly 12 asincluding a K-wire 44 and one or more dilators 46, 48. The K-wire 44 ispreferably constructed having generally narrow diameter (such as, by wayof example only, 1.5 mm) and sufficient rigidity and strength such thatit can pierce the skin of the patient and be advanced through theintervening tissue to reach the surgical target site. The K-wire 44 alsopreferably includes indicia for determining the distance between adistal end 50 and the skin of the patient. The dilators 46, 48 are innerand outer dilating elements, respectively, capable of being sequentiallyintroduced over the K-wire 44 for the purpose of further distracting thetissue previously distracted by the K-wire 44.

The inner dilator 46 is preferably constructed having an inner diameterapproximating the diameter of the K-wire 44 (such as, by way of exampleonly, 1.5 mm), an outer diameter of increased dimension (such as, by wayof example only, 6.5 mm), and indicia for determining the distancebetween a distal end 52 and the skin of the patient. The outer dilator48 is similarly preferably constructed having an inner diameterapproximating the outer diameter of the inner dilator 46 (such as, byway of example only, 6.5 mm), an outer diameter of increased dimension(such as, by way of example only, 9 mm), and indicia for determining thedistance between a distal end 54 and the skin of the patient. Therespective lengths of the K-wire 44 and dilators 46, 48 may varydepending upon the given surgical target site (that is, the “depth” ofthe surgical target site within the patient). It will be similarlyappreciated that the diameters and dimensions for these elements mayalso vary depending upon the particular surgical procedure. All suchsurgically appropriate variations (length, diameter, etc. . . . ) arecontemplated as falling within the scope of the present invention. It isfurther contemplated and within the scope of the present invention thatadditional dilators of increasing diameters may be employed tosequentially dilate to the point where a bladed retractor or retractionassembly may be employed to thereafter create an operative corridoraccording to the present invention (without the need for secondarydistraction as described below).

Referring to FIGS. 5-6, the secondary tissue distraction is preferablyperformed using the pivot linkage assembly 14 in conjunction with thefirst and second distraction arms 16, 18 and first and second speculumblades 20, 22. The speculum blades 20, 22 extend through receivingpassageways 38 (FIG. 6) formed within the first and second distractionarms 16, 18. The handle assembly 24 includes first and second pivot arms60, 62 disposed on one end of the assembly, and third and fourth pivotarms 64, 66 on the opposite end. First and second pivot arms 60, 62 arepivotably coupled via a rod 80 forming part of the locking assembly 32(a locking nut 82 forms the remainder of the locking assembly 32).Second and third pivot arms 64, 66 are pivotably coupled via a rod 84forming part of the locking assembly 34 (a locking nut 86 forms theremainder of the locking assembly 34).

First and second linkage assemblies 70, 72 extend between the distalends of the pivot arms 60-66, each including a pair of linkages 74, 76pivotably coupled together via a rod 78. A ratchet member 68 may be usedto maintain the first pivot arms 60 relative to the second pivot arm 62as they are separated during use. As the pivot arms 60, 62 are movedaway from one another, the first and second distraction arms 16, 18(being coupled to or integrally formed with the linkages 76 of first andsecond linkage assemblies 72, 74) will similarly move away from oneanother. With the speculum blades 20, 22 disposed within the passageways38 (FIG. 5), the relative movement of the pivot arms 16, 18 will causethe speculum blades 20, 22 to move apart and thus perform the desiredsecondary distraction.

The pivot linkage assembly 14 may be constructed from any number ofmaterials suitable for medical applications, including but not limitedto plastics, metals, ceramics or any combination thereof. Depending onthe construction, some or all of the pivot linkage assembly 14 may bedisposable (i.e. single use) and/or reusable (i.e. multi-use).

The speculum blades 20, 22 are generally elongate in nature and includea pair of mating grooves 88 formed along the inwardly facing surfaces ofthe speculum blades 20, 22 which, when mated together, form a lumencapable of passing over the K-wire 44. In a preferred embodiment, thespeculum blades 20, 22 are separable from distraction arms 16, 18 suchthat the blades 20, 22 can be introduced into the patient and thereafterengaged with the handle assembly 24 to effectuate the secondarydistraction. As will be described in greater detail below, thisseparable construction allows the speculum blades 20, 22 to beintroduced down to the surgical target site by passing them through theouter dilator 48 and over with the K-wire 44 (the latter by virtue ofthe lumen formed by the pair of mating grooves 88 along the inwardlyfacing surfaces of the speculum blades 20, 22). This is obviously onlypossible by first removing the inner dilator 46 from within the seconddilator 48 while leaving the K-wire 44 in place. Although shown anddescribed herein as being of separable construction, it will beappreciated by those skilled in the art that the speculum blades 20, 22may be of generally non-separable or fixed construction with the pivotarms 16, 18 of the handle assembly 24.

Retraction

The retraction of the present invention is performed by expanding and/ormodifying the distraction corridor to establish and maintain anoperative corridor to the surgical target site. As shown in FIGS. 7-10,the pivot linkage 14 is configured to receive (and have coupled thereto)a pair of retractor blades 90, 92 of the type shown in FIGS. 9-10. Theretractor blades 90, 92 include a main body element 94 extendingdownwardly and angularly away from a pair of mounting arms 96, 98. Themounting arms 96, 98 are spaced apart from one another so as to create achannel 100 dimensioned to receive the respective rods 80, 84 of thelocking assemblies 32, 34. Once positioned within the channel 100, theretractor blades 90, 92 may be locked in a desired position bytightening the respective nuts 82, 86 of the locking assemblies 32, 34.

In a preferred embodiment, one or more of the retractor blades 90, 92may be equipped with a passageway 102 at or near the distal end of themain body 94, such as by providing a generally planar member 104 alongthe generally curved distal region of the retractor blade 90, 92. Thispassageway 102 is dimensioned to receive a locking member 36 of the typeshown in FIG. 11. The locking member 36 includes a coupling region 106for engagement with an introducer tool 112 (FIG. 8), a main body region108 to be disposed generally within the passageway 102 in use, and adistal region 110 to be introduced into the disc space and engagedbetween the adjacent vertebral bodies to secure the distal ends of theretractor blades 90, 92 during use. In addition to securing theretractor blades 90, 92 relative to the surgical target site, the distalregion 110 also serves to prevent the ingress of unwanted or sensitivebiological structures (e.g., nerve roots and/or vasculature) into thesurgical target site, as well as prevent instruments from passingoutside the surgical target site and contacting surrounding tissues orstructures.

The retractor blades 90, 92 may also be optionally provided with atleast one guard member 114 extending in a curved fashion (and/or,although not shown, in a generally straight fashion) from the distal endof the retractor blade 90, 92. The guard member 114 may be provided, byway of example, for the purpose of preventing tissue (such as nerveroots in spinal surgery applications) from entering into the operativecorridor during surgery and for preventing instruments from extendingoutside the operative corridor and/or the general vicinity of thesurgical target site.

The retractor blades 90, 92 may also be equipped with any number ofdifferent mechanisms for transporting or emitting light at or near thesurgical target site to aid the surgeon's ability to visualize thesurgical target site, instruments and/or implants during the givensurgical procedure. For example, one or more strands of fiber opticcable may be coupled to the retractor blades 90, 92 such that light maybe delivered from a light source and selectively emitted into theoperative corridor and/or the surgical target site. This may beaccomplished by constructing the retractor blades 90, 92 of suitablematerial (such as clear polycarbonate) and configuration such that lightmay be transmitted generally distally through a light exit region formedalong the entire inner periphery of the retractor blade 90, 92 andlocated in the general vicinity as the distal opening of the passageway102. This may be performed by providing the retractor blade 90, 92having light-transmission characteristics (such as with clearpolycarbonate construction) and transmitting the light almost entirelywithin the walls of the retractor blade 90, 92 (such as by frosting orotherwise rendering opaque portions of the exterior and/or interior andcoupling the light source thereto such as via a port) until it exits aportion along the interior of the retractor blades 90, 92 to shine at ornear the surgical target site.

In one embodiment, a variety of sets of retractor blades 90, 92 may beprovided, each having a different length to account for any number ofpossible surgical target sites. In a further embodiment, each set ofretractor blades 90, 92 may be marked or color-coded to aid inindicating to the surgeon the particular length of the blade 90, 92 orthe depth of the surgical target site.

The retractor blades 90, 92 and the locking member 36 may be constructedfrom any number of materials suitable for medical applications,including but not limited to plastics, metals, ceramics or anycombination thereof. Depending on the construction, some or all of thesedevices may be disposable (i.e. single use) and/or reusable (i.e.multi-use).

Any number of suitable mounting units (not shown) may be employed tomaintain the pivot linkage assembly 14 in a fixed and rigid fashionrelative to the patient. By way of example only, this may beaccomplished by providing the mounting unit as a generally U-shapedmounting arm for lockable engagement with the pivot linkage assembly 14,and a coupling mechanism (not shown) extending between the mounting armand a rigid structure (such as the operating table) for maintaining theU-shaped mounting arm in a fixed and rigid position.

Nerve Surveillance

According to yet another aspect of the present invention, any number ofdistraction components and/or retraction components (including but notlimited to those described herein) may be equipped to detect thepresence of (and optionally the distance and/or direction to) neuralstructures during the steps tissue distraction and/or retraction. Thisis accomplished by employing the following steps: (1) one or morestimulation electrodes are provided on the various distraction and/orretraction components; (2) a stimulation source (e.g. voltage orcurrent) is coupled to the stimulation electrodes; (3) a stimulationsignal is emitted from the stimulation electrodes as the variouscomponents are advanced towards or maintained at or near the surgicaltarget site; and (4) the patient is monitored to determine if thestimulation signal causes muscles associated with nerves or neuralstructures within the tissue to innervate. If the nerves innervate, thismay indicate that neural structures may be in close proximity to thedistraction and/or retraction components.

Neural monitoring may be accomplished via any number of suitablefashions, including but not limited to observing visual twitches inmuscle groups associated with the neural structures likely to found inthe tissue, as well as any number of monitoring systems, including butnot limited to any commercially available “traditional” electromyography(EMG) system (that is, typically operated by a neurophysiologist. Suchmonitoring may also be carried out via the surgeon-driven EMG monitoringsystem shown and described in the following commonly owned andco-pending PCT Applications (collectively “NeuroVision PCTApplications”): PCT App. Ser. No. PCT/US02/22247, entitled “System andMethods for Determining Nerve Proximity, Direction, and Pathology DuringSurgery,” filed on Jul. 11, 2002; PCT App. Ser. No. PCT/US02/30617,entitled “System and Methods for Performing Surgical Procedures andAssessments,” filed on Sep. 25, 2002; PCT App. Ser. No. PCT/US02/35047,entitled “System and Methods for Performing Percutaneous PedicleIntegrity Assessments,” filed on Oct. 30, 2002; and PCT App. Ser. No.PCT/US03/02056, entitled “System and Methods for Determining NerveDirection to a Surgical Instrument,” filed Jan. 15, 2003. The entirecontents of each of the above-enumerated NeuroVision PCT Applications ishereby expressly incorporated by reference into this disclosure as ifset forth fully herein.

In any case (visual monitoring, traditional EMG and/or surgeon-drivenEMG monitoring), the access system of the present invention mayadvantageously be used to traverse tissue that would ordinarily bedeemed unsafe or undesirable, thereby broadening the number of mannersin which a given surgical target site may be accessed.

FIGS. 12-13 illustrate, by way of example only, a monitoring system 120of the type disclosed in the NeuroVision PCT Applications suitable foruse with the surgical access system 10 of the present invention. Themonitoring system 120 includes a control unit 122, a patient module 124,and an EMG harness 126 and return electrode 128 coupled to the patientmodule 124, and a cable 132 for establishing electrical communicationbetween the patient module 124 and the surgical access system 10 (FIG.1). More specifically, this electrical communication can be achieved byproviding, by way of example only, a hand-held stimulation controller152 capable of selectively providing a stimulation signal (due to theoperation of manually operated buttons on the hand-held stimulationcontroller 152) to one or more connectors 156 a, 156 b, 156 c. Theconnectors 156 a, 156 b, 156 c are suitable to establish electricalcommunication between the hand-held stimulation controller 152 and (byway of example only) the stimulation electrodes on the K-wire 44, thedilators 46, 46, the speculum blades 20, 22, the retractor blades 90,92, and/or the guard members 114 (collectively “surgical accessinstruments”).

In order to use the monitoring system 120, then, these surgical accessinstruments must be connected to the connectors 156 a, 156 b and/or 156c, at which point the user may selectively initiate a stimulation signal(preferably, a current signal) from the control unit 122 to a particularsurgical access instruments. Stimulating the electrode(s) on thesesurgical access instruments before, during and/or after establishingoperative corridor will cause nerves that come into close or relativeproximity to the surgical access instruments to depolarize, producing aresponse in a myotome associated with the innervated nerve.

The control unit 122 includes a touch screen display 140 and a base 142,which collectively contain the essential processing capabilities(software and/or hardware) for controlling the monitoring system 120.The control unit 122 may include an audio unit 118 that emits soundsaccording to a location of a surgical element with respect to a nerve.The patient module 124 is connected to the control unit 122 via a datacable 144, which establishes the electrical connections andcommunications (digital and/or analog) between the control unit 122 andpatient module 124. The main functions of the control unit 122 includereceiving user commands via the touch screen display 140, activatingstimulation electrodes on the surgical access instruments, processingsignal data according to defined algorithms, displaying receivedparameters and processed data, and monitoring system status and reportfault conditions. The touch screen display 140 is preferably equippedwith a graphical user interface (GUI) capable of communicatinginformation to the user and receiving instructions from the user. Thedisplay 140 and/or base 142 may contain patient module interfacecircuitry (hardware and/or software) that commands the stimulationsources, receives digitized signals and other information from thepatient module 124, processes the EMG responses to extractcharacteristic information for each muscle group, and displays theprocessed data to the operator via the display 140.

In one embodiment, the monitoring system 120 is capable of determiningnerve direction relative to one or more of the K-wire 44, dilationcannula 46, 48, speculum blades 20, 22, the retractor blades 90, 92,and/or the guard members 114 before, during and/or following thecreation of an operative corridor to a surgical target site. Monitoringsystem 120 accomplishes this by having the control unit 122 and patientmodule 124 cooperate to send electrical stimulation signals to one ormore of the stimulation electrodes provided on these instruments.Depending upon the location of the surgical access system 10 within apatient (and more particularly, to any neural structures), thestimulation signals may cause nerves adjacent to or in the generalproximity of the surgical access system 10 to depolarize. This causesmuscle groups to innervate and generate EMG responses, which can besensed via the EMG harness 126. The nerve direction feature of thesystem 120 is based on assessing the evoked response of the variousmuscle myotomes monitored by the system 120 via the EMG harness 126.

By monitoring the myotomes associated with the nerves (via the EMGharness 126 and recording electrode 127) and assessing the resulting EMGresponses (via the control unit 122), the surgical access system 10 iscapable of detecting the presence of (and optionally the distant and/ordirection to) such nerves. This provides the ability to activelynegotiate around or past such nerves to safely and reproducibly form theoperative corridor to a particular surgical target site, as well asmonitor to ensure that no neural structures migrate into contact withthe surgical access system 10 after the operative corridor has beenestablished. In spinal surgery, for example, this is particularlyadvantageous in that the surgical access system 10 may be particularlysuited for establishing an operative corridor to an intervertebraltarget site in a postero-lateral, trans-psoas fashion so as to avoid thebony posterior elements of the spinal column.

FIGS. 14-15 are exemplary screen displays (to be shown on the display140) illustrating one embodiment of the nerve direction feature of themonitoring system shown and described with reference to FIGS. 12-13.These screen displays are intended to communicate a variety ofinformation to the surgeon in an easy-to-interpret fashion. Thisinformation may include, but is not necessarily limited to, a display ofthe function 180 (in this case “DIRECTION”), a graphical representationof a patient 181, the myotome levels being monitored 182, the nerve orgroup associated with a displayed myotome 183, the name of theinstrument being used 184 (in this case, a dilator 46, 48), the size ofthe instrument being used 185, the stimulation threshold current 186, agraphical representation of the instrument being used 187 (in this case,a cross-sectional view of a dilator 46, 48) to provide a reference pointfrom which to illustrate relative direction of the instrument to thenerve, the stimulation current being applied to the stimulationelectrodes 188, instructions for the user 189 (in this case, “ADVANCE”and/or “HOLD”), and (in FIG. 15) an arrow 190 indicating the directionfrom the instrument to a nerve. This information may be communicated inany number of suitable fashions, including but not limited to the use ofvisual indicia (such as alpha-numeric characters, light-emittingelements, and/or graphics) and audio communications (such as a speakerelement). Although shown with specific reference to a dilating cannula(such as at 184), it is to be readily appreciated that the presentinvention is deemed to include providing similar information on thedisplay 140 during the use of any or all of the various instrumentsforming the surgical access system 10 of the present invention,including the initial distraction assembly 12 (i.e. the K-wire 44 anddilators 46, 48), the speculum blades 20, 22 and/or the retractor blades90, 92 and/or the guard members 114.

The initial distraction assembly 12 (FIGS. 2-4) may be provided with oneor more electrodes for use in providing the neural monitoringcapabilities of the present invention. By way of example only, theK-wire 44 may be equipped with a distal electrode 200. This may beaccomplished by constructing the K-wire 44 for a conductive material,providing outer layer of insulation 202 extending along the entirelength with the exception of an exposure that defines the electrode 200.As best shown in FIGS. 3-4, the electrode 200 has an angledconfiguration relative to the rest of the K-wire 44 (such as, by way ofexample only, in the range of between 15 and 75 degrees from thelongitudinal axis of the K-wire 44). The angled nature of the electrode200 is advantageous in that it aids in piercing tissue as the K-wire 44is advanced towards the surgical target site.

The angled nature of the distal electrode 200 is also important in thatit provides the ability to determine the location of nerves or neuralstructures relative to the K-wire 44 as it is advanced towards orresting at or near the surgical target site. This “directional”capability is achieved by the fact that the angled nature of theelectrode 200 causes the electrical stimulation to be projected awayfrom the distal portion of the K-wire 44 in a focused, or directedfashion. The end result is that nerves or neural structures which aregenerally closer to the side of the K-wire 44 on which the electrode 200is disposed will have a higher likelihood of firing or being innervatedthat nerves or neural structures on the opposite side as the electrode200.

The direction to such nerves or neural structures may thus be determinedby physically rotating the K-wire 44 at a particular point within thepatient's tissue and monitoring to see if any neural stimulation occursat a given point within the rotation. Such monitoring can be performedvia visual observation, a traditional EMG monitoring, as well as thenerve surveillance system disclosed in the above-referenced NeuroVisionPCT Applications. If the signals appear more profound or significant ata given point within the rotation, the surgeon will be able tell wherethe corresponding nerves or neural structures are, by way of exampleonly, by looking at reference information (such as the indicia) on theexposed part of the K-wire 44 (which reference point is preferably setforth in the exact same orientation as the electrode 200).

Dilators 46, 48 may also be provided with angled electrodes 204, 206,respectively, for the purpose of determining the location of nerves orneural structures relative to the dilators 46, 48 as they are advancedover the K-wire 44 towards or positioned at or near the surgical targetsite. Due to this similarity in function with the electrode 200 of theK-wire 44, a repeat explanation is not deemed necessary. The dilators46, 48 may be equipped with the electrodes 204, 206 via any number ofsuitable methods, including but not limited to providing electricallyconductive elements within the walls of the dilators 46, 48, such as bymanufacturing the dilators 46, 48 from plastic or similar materialcapable of injection molding or manufacturing the dilators 46, 48 fromaluminum (or similar metallic substance) and providing outer insulationlayer with exposed regions (such as by anodizing the exterior of thealuminum dilator).

According to one aspect of the present invention, additional neuralmonitoring equipment may be employed so as to further preventinadvertent contact with neural structures. For example, after theinitial dilator 46 has been withdrawn in order to subsequently receivethe mated speculum blades 20, 22, a confirmation probe (providing astimulation signal) may be inserted through the outer dilator 48 and toa point at or near the surgical target site. The confirmation probe maythereafter be stimulated for the purpose of double-checking to ensurethat no nerves or neural structures are disposed in the tissue near (orhave migrated into the vicinity of) the distal end 54 of the outerdilator 48 before introducing the speculum blades 20, 22. By confirmingin this fashion, the outer dilator 48 may be removed following theintroduction of the speculum blades 20, 22 and the secondary distractionperformed (by coupling the handle assembly 24 to the blades 20, 22 andexpanding) without fear of inadvertently causing the speculum blades 20,22 to contact nerves or neural structures.

The secondary distraction of the present invention (FIGS. 5-6) may beprovided with one or more electrodes for use in providing the neuralmonitoring capabilities of the present invention. By way of exampleonly, it may be advantageous to provide one or more electrodes along thespeculum blades 20, 22 and/or on the concave region 252 (such asstimulation electrode 208) for the purpose of conducting neuralmonitoring before, during and/or after the secondary distraction.

The retractor blades 90, 92 of the present invention (FIGS. 7-10) mayalso be provided with one or more electrodes for use in providing theneural monitoring capabilities of the present invention. By way ofexample only, it may be advantageous to provide one or more electrodes210 on the guard members 114 and/or the stimulation electrodes 212 onthe locking members 36 (preferably on the side facing away from thesurgical target site) for the purpose of conducting neural monitoringbefore, during and/or after the retractor blades 90, 92 have beenpositioned at or near the surgical target site.

The surgical access system 10 of the present invention may be sold ordistributed to end users in any number of suitable kits or packages(sterile and/or non-sterile) containing some or all of the variouscomponents described herein. For example, the pivot linkage assembly 14may be provided such that the pivot arms 16, 18 and speculum blades 20,22 are disposable and the retractor blades 90, 92 are re-usable. In afurther embodiment, an initial kit may include these materials,including a variety of sets of retractor blades 90, 92 having varying(or “incremental”) lengths to account for surgical target sites ofvarying locations within the patient.

Spine Surgery Example

The surgical access system 10 of the present invention will now bedescribed, by way of example, with reference to the spinal applicationshown in FIG. 16-_. It will, of course, be appreciated that the surgicalaccess system and related methods of the present invention may findapplicability in any of a variety of surgical and/or medicalapplications such that the following description relative to the spineis not to be limiting of the overall scope of the present invention.More specifically, while described below employing the nerve monitoringfeatures described above (otherwise referred to as “nerve surveillance”)during spinal surgery, it will be appreciated that such nervesurveillance will not be required in all situations, depending upon theparticular surgical target site.

FIGS. 16-22 illustrate the method steps involved in using the initialtissue distraction assembly 12 of the present invention. The K-wire 44is first introduced along a given pathway towards the surgical targetsite (which, in this case, is an intervertebral disc level of the lumbarspine). Determining the preferred angle of incidence into the surgicaltarget site (as well as the advancement or positioning of any requiredsurgical instruments (such as the surgical access system of the presentinvention), devices and/or implants) may be facilitated through the useof surgical imaging systems (such as fluoroscopy) as well any number ofstereotactic guide systems, including but not limited to those shown anddescribed in co-pending and commonly owned U.S. patent application Ser.No. 09/888,223, filed Jun. 22, 2001 and entitled “Polar CoordinateSurgical Guideframe,” the entire contents of which is incorporated byreference as if set forth in its entirety herein.

Nerve surveillance is preferably conducted during this step (viaelectrode 200) to monitor for the existence of (and optionally thedistance and direction to) nerves or neural structures in the tissuethrough which the K-wire 44 must pass to reach the surgical target site.According to a preferred embodiment of the present invention, it isgenerally desired to advance the K-wire 44 such the distal electrode 200is disposed a distance anterior to the exiting nerve root 300 (such as,by way of example, 10 mm). As shown in FIGS. 16-17, it is preferred toadvance the K-wire 44 to the annulus 302 of the disc before advancingthe inner dilator 46. This is to prevent the unnecessary distraction ofthe psoas muscle 304 (which must be passed through in order to approachthe surgical target site in the lateral or far-lateral approach shown)in the instance significant nerves or neural structures are encounteredin the initial advancement of the K-wire 44. If such nerves or neuralstructures are encountered, the K-wire 44 may simply be removed andre-advanced along a different approach path.

As shown in FIGS. 18-19, once the K-wire 44 is safely introduced to thesurgical target site, the inner dilator 46 may thereafter be advancedover the K-wire 44 until the distal end 52 abuts the annulus 302 of thedisc. Nerve surveillance is also conducted during this step (viaelectrode 204 shown in FIGS. 3-4) to monitor for the existence of (andoptionally the distance and direction to) nerves or neural structures inthe tissue through which the inner dilator 46 must pass to reach thesurgical target site. Next, as shown in FIG. 22, the K-wire 44 may beadvanced through the annulus 302 such that the electrode 200 is disposedwithin the interior (nucleus pulposis region) of the disc (such as, byway of example, an internal distance of 15 to 20 mm).

With reference to FIGS. 21-22, the outer dilator 48 is next advancedover the inner dilator 46 to further distract the tissue leading down tothe surgical target site. As with the K-wire 44 and inner dilator 46,nerve surveillance is conducted during this step (via electrode 206shown in FIGS. 3-4) to monitor for the existence of (and optionally thedistance and direction to) nerves or neural structures in the tissuethrough which the outer dilator 48 must pass to reach the surgicaltarget site.

With reference to FIG. 23, the inner dilator 48 is next removed, leavingthe K-wire 44 and outer dilator 48 in position. This creates a spacetherebetween which, in one embodiment of the present invention, isdimensioned to receive the speculum blades 20, 22 as shown in FIGS.24-25. To accomplish this step, the speculum blades 20, 22 must bedisposed in an abutting relationship so as to form an inner lumen (viacorresponding grooves 88 shown in FIG. 5) dimensioned to be slideablyadvancing over the stationary K-wire 44. Once again, as noted above, itmay be desired at this step to advance a confirmation probe down theouter dilator 48 to interrogate the tissue surrounding the surgicaltarget site to ensure that no nerves or neural structures are present in(or have migrated into) this vicinity before the speculum blades 20, 22are advanced into the outer dilator 48.

Turning to FIGS. 26-27, the outer dilator 48 may then be removed,leaving the speculum blades 20, 22 in abutting relationship within thetissue previously distracted by the outer dilator 48. As shown in FIGS.28-29, the pivot linkage assembly 14 may be advanced such that the pivotarms 16, 18 slideably (or otherwise) pass over the speculum blades 20,22. In one embodiment, the pivot arms 16, 18 are dimensioned such thateach distal end comes into general abutment with the exterior of thepsoas muscle 304. That said, it is within the scope of the invention toprovide the pivot arms 16, 18 such that each distal end extends downwardinto the psoas 304 towards the surgical target site (which may beadvantageous from the standpoint of adding rigidity to the distalportions of the speculum blades 20, 22 for the purpose of facilitatingthe process of secondary tissue distraction). Once positioned over thespeculum blades 20, 22, the handle assembly 24 may be operate todistract tissue from the position shown in FIG. 28 to that shown in FIG.29.

As shown in FIG. 30, the first retractor 90 is then introduced into thedistracted region, positioned adjacent to the posterior region of thedisc space, and locked to the pivot linkage 14 via the locking assembly32. At that point, the locking member 36 may be advanced via the tool112 and engaged with the retractor blade 90 such that the middle region108 resides at least partially within the passageway 102 and the distalregion 110 extends into the disc space. Thereafter, as shown in FIG. 31,the retractor blade 92 may be introduced into the distracted region,positioned adjacent to the anterior region of the disc space, and lockedto the pivot linkage 14 via the locking assembly 34. At that point,another locking member 36 may be engaged in the same fashion as with theretractor blade 90, with the distal region 110 extending into the discspace. As shown in FIG. 32, additional retractor blades 91, 93 may becoupled to the pivot linkage 14 to provide retraction in the caudal andcephalad directions, respectively.

The end result is shown in FIG. 33, wherein an operative corridor hasbeen created to the spinal target site (in this case, the disc space)defined by the retractor blades 90, 92 (and optionally 91, 93). Thedistal regions 110 of the locking each locking member 36 advantageouslyextends into the disc space to prevent the ingress of tissue (e.g.,neural, vasculature, etc. . . . ) into the surgical target site and/oroperative corridor and the egress of instruments or implants out of thesurgical target site and/or operative corridor.

In a further protective measure, each retractor blade 90, 92 is equippedwith a guard member 114 to prevent similar ingress and egress. Bothguard members 114 (as well as additional regions of the distal region110 of the locking member 36) may be provided with electrodes 210, 212,respectively, capable of performing nerve surveillance to monitor forthe existence of (and optionally the distance and direction to) nervesor neural structures in the tissue or region surrounding or adjacent tothese components while disposed in the general vicinity of the surgicaltarget site. The electrode 210 on the guard member 114 of the posteriorretractor blade 90, in particular, may be used to assess the status orhealth of the nerve root 300, especially if the nerve root 300 is inclose proximity to that guard member 114. This may be performed by usingthe nerve status determination systems or techniques disclosed inco-pending and commonly assigned U.S. Pat. No. 6,500,128, entitled“Nerve Proximity and Status Detection System and Method,” the entirecontents of which is hereby incorporated by reference as is set forthfully herein.

As evident from the above discussion and drawings, the present inventionaccomplishes the goal of providing a novel surgical access system andrelated methods which involve creating a distraction corridor to asurgical target site, thereafter retracting the distraction corridor toestablish and maintain an operative corridor to the surgical targetsite, and optionally detecting the existence of (and optionally thedistance and/or direction to) neural structures before, during and/orafter the formation of the distraction and/or operative corridors.

The steps of distraction followed by retraction are advantageous becausethey provide the ability to more easily position an operativecorridor-establishing device through tissue that is strong, thick orotherwise challenging to traverse in order to access a surgical targetsite. The various distraction systems of the present invention areadvantageous in that they provide an improved manner of atraumaticallyestablishing a distraction corridor prior to the use of the retractionsystems of the present invention. The various retractor systems of thepresent invention are advantageous in that they provide an operativecorridor having improved cross-sectional area and shape (includingcustomization thereof) relative to the prior art surgical accesssystems. Moreover, by optionally equipping the various distractionsystems and/or retraction systems with one or more electrodes, anoperative corridor may be established through (or near) any of a varietyof tissues having such neural structures which, if contacted orimpinged, may otherwise result in neural impairment for the patient.

The surgical access system of the present invention can be used in anyof a wide variety of surgical or medical applications, above and beyondthe spinal applications discussed herein. By way of example only, inspinal applications, any number of implants and/or instruments may beintroduced through the working cannula 50, including but not limited tospinal fusion constructs (such as allograft implants, ceramic implants,cages, mesh, etc.), fixation devices (such as pedicle and/or facetscrews and related tension bands or rod systems), and any number ofmotion-preserving devices (including but not limited to nucleusreplacement and/or total disc replacement systems).

While certain embodiments have been described, it will be appreciated bythose skilled in the art that variations may be accomplished in view ofthese teachings without deviating from the spirit or scope of thepresent application. For example, with regard to the monitoring system120, it may be implemented using any combination of computer programmingsoftware, firmware or hardware. As a preparatory act to practicing thesystem 120 or constructing an apparatus according to the application,the computer programming code (whether software or firmware) accordingto the application will typically be stored in one or more machinereadable storage mediums such as fixed (hard) drives, diskettes, opticaldisks, magnetic tape, semiconductor memories such as ROMs, PROMs, etc.,thereby making an article of manufacture in accordance with theapplication. The article of manufacture containing the computerprogramming code may be used by either executing the code directly fromthe storage device, by copying the code from the storage device intoanother storage device such as a hard disk, RAM, etc. or by transmittingthe code on a network for remote execution. As can be envisioned by oneof skill in the art, many different combinations of the above may beused and accordingly the present application is not limited by the scopeof the appended claims.

What is claimed is:
 1. A system for accessing a spinal disc of a lumbarspine through an operative corridor, comprising: a distraction assemblyto create a tissue distraction corridor to a lumbar spine, wherein saiddistraction assembly comprises: an elongate inner member deliverabletoward a spinal disc along a lateral, trans-psoas path to the lumbarspine, and at least two supplemental dilators of sequentially largerdiameter deliverable to the spinal disc along the lateral, trans-psoaspath to the lumbar spine, a first supplemental dilator of the at leasttwo dilators having a lumen configured to slidably receive the elongateinner member, a second supplemental dilator of the at least two dilatorsbeing advanceable over the first supplemental dilator along the lateral,trans-psoas path to the lumbar spine, wherein at least one instrumentfrom the group consisting of the elongate inner member, the firstsupplemental dilator, and the second supplemental dilator includes astimulation electrode to deliver electrical stimulation for nervemonitoring when said stimulation electrode is positioned in the lateral,trans-psoas path to the lumbar spine; and a retraction assemblycomprising a plurality of retractor blades to enlarge the tissuedistraction corridor and maintain a trans-psoas operative corridor alongthe lateral, trans-psoas path to the lumbar spine when the plurality ofretractor blades are delivered to the lumbar spine, the retractionassembly further comprising a blade holder apparatus that is configuredto retain the plurality of retractor blades in a selected position tomaintain the trans-psoas operative corridor that is so dimensioned topass a spinal implant through the trans-psoas operative corridor alongthe lateral, trans-psoas path to the lumbar spine.
 2. The system ofclaim 1, further comprising a first extension member to releasably andslidably engage with a first retractor blade of the plurality ofretractor blades so that a distal portion of the first extension memberextends distally from the first retractor blade.
 3. The system of claim2, wherein the distal portion of the first extension member isconfigured to anchor into the lumbar spine when the plurality ofretractor blades are delivered to the lumbar spine.
 4. The system ofclaim 3, wherein when the plurality of retractor blades are delivered tothe lumbar spine, the distal portion of the first extension member isadapted to anchor into the spinal disc between adjacent vertebral bodiesand secures its respective retractor blade relative to the adjacentvertebral bodies.
 5. The system of claim 2, wherein the distal portionof the first extension member comprises a narrowed tip portion that issmaller than a proximal region of the first extension member.
 6. Thesystem of claim 2, further comprising a second extension member toreleasably and slidably engage with a second retractor blade of theplurality of retractor blades so that a distal portion of the secondextension member extends distally from the second retractor blade. 7.The system of claim 1, wherein the retractor assembly further comprisesa plurality of light emitting devices to direct light through theoperative corridor toward the spinal disc, the plurality of lightemitting devices being coupled to the plurality of retractor blades. 8.The system of claim 1, wherein the plurality of retractor bladescomprises a first retractor blade and a second retractor blade that isspaced apart from the first retractor blade when the plurality ofretractor blades enlarge the tissue distraction corridor to form thetrans-psoas operative corridor along the lateral, trans-psoas path tothe lumbar spine.
 9. The system of claim 8, wherein the first retractorblade is a posterior-most retractor blade when the plurality ofretractor blades are delivered to the lumbar spine, further comprising afixation member to releasably engage with the posterior-most blade andto anchor into the lumbar spine when the posterior-most blade isdelivered to the lumbar spine.
 10. The system of claim 1, wherein thestimulation electrode of said at least one instrument comprises anexposed electrode surface positioned on a tapered distal tip portion ofsaid at least one instrument.
 11. The system of claim 10, wherein eachof the elongate inner member, the first supplemental dilator, and thesecond supplemental dilator comprises a corresponding stimulationelectrode positioned on a respective tapered distal tip portion of therespective one of the elongate inner member, the first supplementaldilator, and the second supplemental dilator.
 12. The system of claim 1,wherein the distraction assembly further comprises a secondarydistraction assembly.
 13. The system of claim 12, wherein the secondarydistraction assembly comprises a speculum instrument that is slidablealong the dilator system to prepare the tissue distraction corridor forreceipt of the plurality of retractor blades.
 14. The system of claim 1,wherein each retractor blade of the plurality of retractor blades issequentially advanced along the lateral, trans-psoas path to thetargeted spinal site.
 15. The system of claim 1, wherein each retractorblade of the plurality of retractor blades comprises a stimulationelectrode to deliver electrical stimulation for nerve monitoring. 16.The system of claim 1, further comprising a monitoring system thatdelivers an electrical stimulation signal to the stimulation electrodeof said at least one instrument, and monitors electromyographic activitydetected by a set of sensor electrodes in muscle myotomes associatedwith nerves in the vicinity of the spinal disc.
 17. The system of claim16, wherein the monitoring system displays to a user a numericstimulation threshold value in units of milliAmps while alsocontemporaneously displaying myotome levels being monitored, the numericstimulation threshold being an electrical current value required toobtain the electromyographic activity in at least one of said musclemyotomes.
 18. The system of claim 16, wherein the monitoring systemcomprises a control unit having a video display device, a patient moduleconnected to the control unit via a data cable, an EMG sensor harnesshaving the set of sensor electrodes connected to the patient module, andwherein the control unit receives signals from the patient module andprocesses EMG responses output from the sensor electrodes to extractcharacteristic information for each of said muscle myotomes.
 19. Thesystem of claim 1, wherein the elongate inner member has a first length,the first supplemental dilator has a second length less than the firstlength of the elongate inner member, and the second supplemental dilatorhas a third length less than the second length of the first supplementaldilator.
 20. The system of claim 1, wherein the elongate inner membercomprises a guide wire instrument.